1. Field of the Invention
The present invention generally relates to a fuel vapor treatment system. More specifically, the present invention relates a fuel vapor treatment system equipped with a failure diagnosis apparatus.
2. Background Information
Engines are provided with a fuel vapor treatment apparatus or system (called an evaporation control system) that temporarily adsorbs fuel vapor generated inside the fuel tank in a canister, and then opens a purge valve when the engine enters a prescribed operating region to direct the fuel vapor adsorbed in the canister to the intake passage of the engine.
Such a fuel vapor treatment system sometimes has a diagnostic device for the purpose of detecting leaks in the piping and other components of the fuel vapor treatment system. The diagnostic device often uses the negative intake pressure of the engine to pull the fuel vapor treatment system to a negative pressure. The diagnostic device holds the system in a closed off state, monitors the change in pressure within the fuel vapor treatment system, and determines that there is an abnormality in the piping or components of the fuel vapor treatment system if the change in pressure is greater than or equal to a prescribed value. However, if the atmospheric pressure changes during the course of this leak diagnosis, the pressure inside the fuel vapor treatment system cannot be measured accurately.
Therefore, there are leak diagnosis devices that have an atmospheric pressure sensor in addition to the sensor that measures the pressure inside the fuel vapor treatment system. These leak diagnosis devices conduct the leak diagnosis by measuring both the atmospheric pressure and the pressure inside the fuel vapor treatment system. There are also leak diagnosis devices that have a selector valve in a pipe that connects to the fuel vapor treatment system and conduct the leak diagnosis by using the selector valve to selectively direct the pressure inside the fuel vapor treatment system and the atmospheric pressure to a pressure sensor. Examples of such fuel vapor treatment systems are disclosed in Japanese Laid-Open Patent Publication Nos. 2000-282970, 10-37813, and 07-317611.
In view of the above, there exists a need for an improved failure diagnosis apparatus for a fuel vapor treatment system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discover that using of a plurality of sensors increases the cost of the fuel vapor treatment system. Also it has been discover that using a selector valve in order to measure the atmospheric pressure and the pressure inside the fuel vapor treatment system makes the structure of the system more complex and results in an inability to reduce cost.
Also, the prior art has also been problematic in that a misdiagnosis will occur if the relief valve provided on the filler cap of the fuel tank opens during the leak diagnosis.
An object of the present invention is to provide a fuel vapor treatment system that solves these problems.
In accordance with one aspect of the present invention, a fuel vapor treatment system is provided with a fuel tank, a canister, a purge valve, a drain cut valve, an absolute pressure sensor and a failure diagnosis control device. The canister is fluidly coupled to the fuel tank and configured to adsorb fuel vapor evaporated from the fuel tank. The purge valve is disposed to open and close piping that fluidly couples the canister to an intake passage of an internal combustion engine into which fuel vapor flows from the canister. The drain cut valve operatively coupled to the canister to open and close an atmospheric release port of the canister. The absolute pressure sensor is configured and arranged to detect absolute pressure inside the fuel vapor treatment system and measure atmospheric pressure based on an open-closed statuses of the drain cut valve and the purge valve. The failure diagnosis control device is configured and arranged to close off a portion of the fuel vapor treatment system between the fuel tank and the purge valve and conduct a leak diagnosis when a permisssion condition is met. The leak diagnosis control device is configured to conduct the leak diagnosis based on the atmospheric pressure and the change in pressure inside the portion of the fuel vapor treatment system while the portion of the fuel vapor treatment system is closed off.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.